1. Field Of The Invention
The invention relates to an internal-gear pump for pumping fuel in an internal combustion engine, having an internal-toothed annular gear and an external-toothed pinion that cooperates with the annular gear to generate a pumping action.
2. Description Of The Prior Art
An internal-gear pump of the type with which this invention is concerned is also known as an annular gear pump or gear-rotor pump. The annular gear and the pinion are the pump elements and are also called an outer rotor and inner rotor. German Patent Disclosure DE 38 27 573 A1 describes an internal-gear pump whose annular gear is driven via an electric motor. The pumping chambers of the internal-gear pump that are located between the sets of teeth of the two pump elements are covered in the axial direction by a thrust washer. A helical spring embodied as a compression spring, which is prestressed against the pressure plate assures that the axial play is zero upon starting of the engine.
An object of the invention is to increase the pump capacity at the starting rpm and to lengthen the service life of the internal-gear pump described at the outset. It should also be possible to produce the internal-gear pump economically.
In an internal-gear pump for pumping fuel in an internal combustion engine, having an internal-toothed annular gear and an external-toothed pinion that cooperates with the annular gear to generate a pumping action, this object is attained in that the pinion is supported radially movably, eccentrically to the annular gear, on a bearing journal, and that a device is provided in order to compensate for the radial play between the pinion and the annular gear, especially upon starting of the engine.
Upon engine starting, the pressure in the internal-gear pump is equal to zero. By means of the spring device according to the invention, the end play between two teeth of the pump elements meshing with one another is compensated for upon engine starting. Once the idling rpm is reached, the pump pressure rises and acts counter to the spring force. As a result, the radial play increases, causing the pump capacity to drop and improving the tribological conditions in the pump by increasing the end play.
A particular embodiment of the invention is characterized in that on the circumference of the bearing journal, two flat faces are embodied, which are disposed essentially parallel to the eccentric axis of the internal-gear pump and serve to guide a bearing bush for the pinion in the radial direction. The two flat faces also serve to guide a sealing plate axially for sealing off the pumping chambers of the pump and to secure against a rotary motion of the sealing plate.
A further particular embodiment of the invention is characterized in that the device is formed by a leaf spring with two legs disposed essentially at right angles to one another, one leg being disposed on the face end of the bearing journal and the other leg being disposed between the bearing journal and a bearing bush for the pinion. The spring device is fixed in the built-in state by the leg resting on the bearing journal. The other leg of the spring device serves to compensate for the radial play.
A further particular embodiment of the invention is characterized in that the leg of the leaf spring disposed between the bearing journal and the bearing bush for the pinion is embodied as curved in the longitudinal direction and/or the transverse direction. Embodying the leg as curved assures improved spring action of the leaf spring. The leaf spring can be embodied as singly or multiply curved.
A further particular embodiment of the invention is characterized in that the device is formed by a helical spring, which is disposed between the bearing journal and a bearing bush for the pinion. An indentation for receiving part of the helical spring may be embodied in the bearing journal, in order to keep the helical spring in position in the built-in state.
A further particular embodiment of the invention is characterized in that a stop for the bearing bush is embodied on the bearing journal. The stop serves to limit the radial play after the starting process.
A further particular embodiment of the invention is characterized in that the device for compensating for the radial play is formed by a slit that extends in the longitudinal direction of the bearing journal. Thus in an especially simple way, an elasticity of the bearing journal in the radial direction is made possible. The aforementioned bearing bush and the spring can be dispensed with.
A further particular embodiment of the invention is characterized in that the device for compensating for the radial play is formed by an elongated recess with a chamfer against which a ball is prestressed with the aid of a spring. The more strongly the ball is pressed against the chamfer, the less is the radial play between the pinion and the annular gear. The recess in the bearing journal is designed such that the ball rests both on the bearing journal and on the inner circumference of the bearing bush.
A further particular embodiment of the invention is characterized in that the prestressing force of the spring is adjustable with the aid of a screw. For instance, the screw can be guided in a threaded bore in the housing of the internal-gear pump. By rotating the screw, the prestressing force of the spring and thus the radial play between the pinion and the annular gear can be continuously variably adjusted.
A further particular embodiment of the invention is characterized in that the pinion is coupled to a drive shaft by an Oldham coupling or a radially elastic coupling. An axial offset that may be present between the drive shaft and the bearing journal can be compensated for by the Oldham coupling. The Oldham coupling, which is also known as a cross-disk coupling, moreover makes the radial motion of the pinion required to compensate for the radial play possible.